It is routine for gas turbine engines to have to pass stringent vibration acceptance tests following production. Rotor eccentricities are a main source of engine vibration, and eccentricities can be alleviated by rotor balancing. Balancing is the act of aligning the masses arid rotational centers of the rotor assembly. Complicating matters greatly is the fact that gas turbine, engine rotors typically comprise a plurality of rotors, such as multiple compressor or turbine stages, which are bolted or clamped together. The prior art approaches to rotor balancing have had reasonable success with simple rotors, but not as much with complicated rotors of the type found in gas turbine engines. So, while methods and apparatuses already exist for assisting in gas turbine rotor balancing, errors present in these approaches can tend to be magnified by the complicated rotor designs, and thus present a risk, that an engine will not meet test requirements despite having been balanced according to prior art techniques. If an engine does not pass the vibration acceptance limit, it typically must be disassembled, re-balanced, and reassembled, which wastes time and resources. Accordingly, there is a need to provide improvements to rotor assembly.